Look at your 42T ring. If the gaps between the teeth are almost down to the bolt circle, you have a 144mm BCD, and the smallest you can go is 41T, assuming you can find one.
If that is the case, just replace that 13-23 in back with a 14-24, or something larger if your rear derailleur can take it. For a 2x6 setup, I use 50-42/14-26 or 46-38/13-25 for a 1.5-step, or 45-42/13-26 for half-step. A low in the low 40s and a high in the mid 90s provide all the range I need.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069